AVS 52nd International Symposium
    Technology for Sustainability Tuesday Sessions
       Session TS-TuM

Paper TS-TuM4
Direct Oxidation of Hydrocarbon Fuels in a Solid Oxide Fuel Cell: Studies of Carbon Formation

Tuesday, November 1, 2005, 9:20 am, Room 313

Session: Fuel Cells, Hydrogen Economy, Sustainable Manufacturing
Presenter: E.M. Stuve, University of Washington
Authors: V.K. Medvedev, University of Washington
L.M. Roen, University of Washington
E.M. Stuve, University of Washington
Correspondent: Click to Email
Solid oxide fuel cells (SOFC) provide an opportunity for fuel-flexible fuel cells that operate at higher efficiencies than other types of fuel cells. These advantages arise from the high temperature of SOFC operation, 800-1000 °C, which facilitates direct oxidation and reforming of hydrocarbon fuels and a source of high quality waste heat. This work examines direct oxidation of hydrocarbon fuels on a SOFC installed in a vacuum system with facilities for accurate measurement of fuel and oxygen partial pressures and measurement of reaction products by a calibrated mass spectrometer. The measurements highlight the interplay of fuel oxidation kinetics, carbon deposition on the anode, and transport of oxide ions through the electrolyte. The SOFC consisted of a Gd-doped ceria electrolyte (Gd@sub 0.1@Ce@sub 0.9@O@sub 2@) with platinum anode and cathode. Fuels of study included methanol, ethanol, methane, ethylene, carbon monoxide, and hydrogen. The reactions were studied over the temperature range of 800-1000 °C with fuel and oxygen partial pressures of 0-10 Torr and 0-70 Torr, respectively. Hydrogen, CO, methanol, and ethanol showed similar reaction characteristics, with high open circuit voltages of 0.6 V and above and maximum current densities of approximately 2 mA/cm@super 2@. By contrast, ethylene and methane showed much slower reaction rates, with open circuit voltages of approximately 0.1 V and maximum current densities of approximately 0.01 mA/cm@super 2@. Post-reaction titration of the anode surface with oxygen showed evidence of extensive carbon formation under the low reaction conditions. The dynamic response of the system under changing fuel and oxygen partial pressures provided further evidence of carbon formation. These experiments help establish the mechanism of direct fuel oxidation in solid oxide fuel cells and the conditions for avoiding carbon deposition on the anodes. This work was supported by the Office of Naval Research.